This invention relates to a telecommunication system and in particular it relates to UMTS (Universal Mobile Telecommunications System).
Under UMTS proposals, a mobile station (MS) can be connected via radio interface both as an IP (Internet Protocol) terminal and as a traditional phone terminal. With an IP connection and the associated Quality of Service, QoS, mechanism, a terminal can make and receive a voice call via the packet-switch domain.
In order for an MS to receive a VoIP (Voice over Internet Protocol) call, it has to have an IP address assigned so that it can receive call setup messages and media streams over IP. However, under current UMTS specifications, a UMTS core network (CN) can initiate a PDP (Packet Data Protocol) context set up only for static IP addresses. This is because only the home gateway GPRS Support Node (GGSN) associated with the static IP address holds the IP to IMSI (International Mobile Subscriber Identity) address mapping required to contact the home location register (HLR), where GPRS denotes General Packet Radio System. When dynamic IP addressing is used and when an MS is not in an active PDP context, the network cannot initiate a PDP context set up and therefore the MS cannot receive calls.